Mercury-metallic halide vapor lamp with regenerative cycle



July 21, 1970 P. D. JOHNSON MERCURY-METALLIC HALIDE VAPOR LAMP WITHREGENERATIVE CYCLE Filed Sept. 25. 196?- I? vervjo/r: 7 a er'D. o nsoh,by 624% i Attorney.

United States Patent 01 lice 3,521,110 Patented July 21, 1970 3,521,110MERCURY-METALLIC HALIDE VAPOR LAMP WITH REGENERATIVE CYCLE Peter D.Johnson, Schenectady, N.Y., assignor to General Electric Company, acorporation of New York Filed Sept. 25, 1967, Ser. No. 670,096 Int. Cl.H01j 17/20, 61/18 U.S. Cl. 313227 6 Claims ABSTRACT OF THE DISCLOSUREThe present invention relates to vapor arc discharge lamps of the typecontaining mercury and one or more vaporizable metallic halides whichare dissociated in the heat of an arc between a pair of primaryarc-electrodes extending into an evacuable envelope. More particularly,the present invention relates to such vapor arc discharge lamps whereinthe evaporation and sputtering of electrode materials from theare-electrodes to the interior of the bulb wall in the vicinity of theelectrodes is counteracted by an improved regenerative halidevapor-transport cycle which maintains the wall metal-free and greatlyincreases the life of the arc-electrodes.

Improved vapor-arc discharge lamps for the production of high-intensity,high-eificiency, near white light have been made possible :by theinvention of the mercurymetallic halide, vapor-arc discharge lamp as isset forth in U.S. Pat. No. 3,234,421 to G. H. Reiling, issued Feb. 8,1966'.

In accord with the teachings of the Reiling patent, the emission of avapor-arc lamp is obtained from the linebroadened spectra of one or moremetals included within the lamp envelope as the halide thereof,generally of the alkali or alkaline earth metals to which has been addedcolor-compensating metal halides such as gallium, indium, thallium, andcertain rare earth metals, to produce a pleasing, white emission of highintensity.

In the development of this type of lamp, it has been found that certainother materials, as for example, rare earth metals, thorium, vanadium,scandium, and the like, also can contribute to the production ofhigh-efficiency white light or light of a preselected wavelength inaccord with the mechanism described and claimed in the aforementionedReiling patent.

While such lamps are of great utility and have constituted along-awaited break-through in the area of vaporarc illumination, certainproblems still exist. One such problem relates to a phenomenon which isexperienced in practically all electric discharge devices, namely, thedepreciation of the light emission characteristics and, in manyinstances, the eventual failure of the lamp, due to the sputteringand/or evaporation of metallic particles, from the electrodes orfilament contained within the lamps. This metallic matter removed fromthe electrodes deposits upon the envelope wall in the vicinity of theelectrodes, causing the light-transmitting characteristics of the lampenvelope to be decreased. Additionally, the removal of filament orarc-electrode material often causes eventual failure of the lamp byfailure of the filament or electrode. In vapor-arc discharge lamps, suchphenomenon results in the darkening of the envelope wall in the vicinityof the primary arc-electrodes and may contribute to eventual failure ofthe arc-electrodes.

Accordingly, it is an object of the present invention to provideimproved vapor-arc discharge lamps having improved light transmissivecharacteristics.

Another object of the present invention is to provide electric vapor-arcdischarge lamps having improved lighttransmissive characteristics andlong arc-electrode life.

Still another object of the present invention is to provide improvedmercury-metallic halide lamps wherein removal of arc-electrode materialand the deposition thereof upon the inner wall of the lamp envelope iscounteracted.

In accord with one embodiment of the present invention, I provide amercury-metallic halide vapor-arc discharge lamp having an evacuableenvelope containing a pair of non-liquid arc-electrodes and a charge,including a quantity of mercury, suflicient upon complete evaporationthereof, to provide a partial pressure of mercury of approximately /2 to10 atmospheres. Also within the envelope, I provide a charge oflight-emitting material including at least the vaporizable halide, otherthan the fluoride, of sodium with or without one or more dissociable,vaporizable light-emitting halides which like the sodium halide aredissociated to cause the production of light by excitation of themetallic species thereof. In addition to the foregoing halides, Iprovide a quantity of polyvalent metallic halide, other than thefluoride, of a metal other than the alkaline metals, the alkaline earthmetals, the rare earth metals, and the transition metals, which halideis at least partially dissociated at the operating temperature of theenvelope wall to provide thereat a specie, either a subhalide compoundor free halogen, which is able to react with any vaporized or sputteredarc electrode material which is deposited on the bulb walls and, bymeans of the regenerative halide cycle, return the deposited metal tothe arc-electrode from whence it came. This regenerative cycle preventsthe deterioration of the transmissive characteristics of the bulb walland the eventual deterioration and failure of the arc-electrodes.

The novel features believed characteristic of the present invention areset forth in the appended claims. The invention itself, together withfurther objects and advantages thereof, may best be understood byreference to the following detailed description, taken in connectionwith the appended drawing in which,

A vapor arc discharge lamp constructed in accord with the teachings ofthe present invention is illustrated in vertical view with parts brokenaway.

In the drawing, a mercury-metallic halide vapor-arc discharge lampconstructed in accord with the present invention includes an exterior,evacuable, light-transmissive envelope I mounted upon a screw typecontact-making base 2, and including therein an inner arc-containingenvelope 3. Inner envelope 3 is light-transmissive; generallycylindrical in shape; hermetically-sealed; and is terminated withpinched-off sections 4 and 5 at the upper and lower ends thereof, whichpinched-off sections serve both to hermetically seal the inner envelopeas it is fabricated from a tubular member and to make appropriate sealswith the lead-in wires to the electrodes contained therein as they passtherethrough. Envelope 1 may be of any suitablehigh-temperature-resistant light-transmissive substance, as for examplePyrex or Vycor glass. Envelope 3 may be of any similarlight-transmissive, but higher-temperature-resistant material, such asfused quartz, Lucalox (U.S. Pat. 3,026,210) or high-density yttria asdisclosed and claimed in the copending application of -R. C. Anderson,Ser. No. 582,755, filed Sept. 28, 1966, and assigned to the presentassignee.

A pair of arc-electrodes 6 and 7, which may conveniently comprise coiledhelical members of tungsten wire or thoriated tungsten wire, or tungstenwire with a sliver of thorium contained therein, or coiled-coil helices,thereof, as is well known in the lamp art technology, are centrallylocated within interior envelope 3 at opposed ends thereof.Arc-electrodes '6 and 7 are spaced a sufficient distance apart so as tosustain a high-current electric arc therebetween for the vaporization ofthe vaporizable constituents contained therein and the production ofhigh intensity radiation of appropriate wave lengths. Arc-electrodes 6and 7 are supported upon electrode leadin members 8 and 9 respectively,which are sealed through pinched regions 4 and respectively, in hermeticseal. A starting electrode 10 is located within one end of innerenvelope 3 and is sealed through pinched region 5 of inner envelope 3.Starting electrode 10 is connected through a resistance 11 to a lead andsupport member 12 which is at the same electrical potential with anotherlead and support member 13, both of which are connected to one contactmember of connecting base 2. It will be appreciated, however, that othermeans than starting electrode 10 may be utilized to start the lamp.

Inner envelope 3 is suspended within outer envelope 1 by means of asimple set of saddle-clamp members 14 and which are dependent from leadand support member 13 and which are securely mechanically fastened aboutthe flattened portions of pinched regions 4 and 5 of inner envelope 3.Lower saddle clamp 14 is connected between support members 12 and 13 andupper saddle clamp 15 is connected between support member 13 and asuspended support member 16 which is connected with a collar 17 whichfits over a reentrant nipple 18 within the upper portion or exteriorbulb member 1, which collar 16 serves to anchor the upper end of leadand support member 13. ()ne arc-electrode 6 is connected to supportmember 13, while the other arc-electrode 7 is connected to a separatelead which is connected to the contact member of screw base 2 remainingafter lead and support member 13 and 12 are connected to thefirstmentioned contact member thereof.

Envelope 3 contains a filler substance 19 which exists in the form of aglobule, containing for example, the solid constituents containedtherein during the quiescent, nonoperating condition of the lamp. Theglobule is composed primarily of sufficient mercury, so that upon theattainment of suitable operating temperature conditions, the mercury istotally volatilized and the vapor thereof pro duces a mercury pressurewithin envelope 3 of approximately to 10 atmospheres. It is essential inthe operation of lamps in accord with the present invention, as well asthe lamp of the aforementioned Reiling patent, the disclosure of whichis incorporated herein by reference thereto, that, at operatingtemperatures and pressures of the order of one atmosphere or greater,that no remaining mercury exists in the liquid state within envelope 3.This is because the operating temperature that is required to volatilizethe remaining constituents of globule 19 is substantially higher thanthat which may be obtained if an equilibrium exists between a liquid andvapor phase of mercury within envelope 3. Thus for example, since theboiling point of mercury at atmospheric pressure is approximately 355C., if any liquid mercury remains in the inner envelope 3 duringoperation, that temperature is the maximum equilibrium temperature whichmay exist within the envelope. Accordingly, the quantity of mercury inglobule 19 is so established as to insure complete volatilizationthereof, so that the high operating temperatures required forvolatilization of the remaining constituents of filler 19 may beobtained.

Filler 19 also includes one or more dissociable metallic halides otherthan fluoride, which are at least partially volatilized at the operatingtemperature created by the initial volatilization of mercury and theestablishment of a mercury arc discharge between arc-electrodes 6 and 7.

It has been found that for the production of high efficiency,chromatically satisfactory light from mercurymetallic halide lamps inaccord with the present invention, the presence of an alkali metalhalide, preferably a sodium halide such as sodium iodide, sodiumbromide, or sodium chloride is required. Since the light emitted by thealkali halides, and particularly the sodium halides, is generally withinthe long wavelength portion of the visible spectrum generally in theyellow or red, it is generally desired, for the production of achromatically pleasing or near-white light, that other metallic halideswhich are also subject to dissociation and light emission, but whichemit light in the shorter wavelength portion of the spectrum, beutilized as a part of filler 19. Thus, for example, ideal near-whitelight having a lumen efiiciency of approximately lumens per watt may beobtained utilizing, as light-emitting constituents, the iodides ofsodium, thallium, and indium. The amount of each halide added dependsupon the vapor pressure and the dissociation characteristics of thehalide. Thus, for example, for a halide which has a relatively low vaporpressure, as for example sodium halide, a suflicient quantity is supplied so that an excess of sodium halide exists within the charge underequilibrium conditions. With other halides, as for example, galliumiodide, which has a relatively high vapor pressure, and is completelyvolatilized at the operating temperatures of the lamp, a sufficientquantity is provided so that the partial pressure caused by-thevolatilization of the particular halide varies in a range ofapproximately 0.1 to 200 torr of the particular halide. If a pluralityof halides are utilized, the partial pressure of each attained withinthe lamp should be a pressure of from 0.1 to 200 torr of each halide.

In the operation of this type of lamp, the bulb walls are located at adistance with respect to the arc-electrodes and the distance between thearc-electrodes is adjusted so that the normal operating condition of thelamp causes the temperature of the inner surface of envelope 3 to begreater than 600 C. and no greater than 1200 C. at its coldest portion.In general, the coldest portion thereof is generally that portion at theextreme end thereof behind the arc-electrodes. For this reason, it isoften found desirable to coat the ends of envelope 3 in the vicinity ofthe arc-electrodes with a reflecting substance so that light radiatedtoward the end of the lamp is focused back upon the electrode thuskeeping that portion of the lamp at a higher temperature than if theradiation were to pass through the ends of the lamp.

Envelope 3 also contains a filling or buffer gas for initial starting ofthe lamp. Such a filling or buffer gas may, for example, be from 10 to25 torr partial pressure of an inert gas, as for example argon, whichhas a relatively low break-down potential.

The general mode of operation of mercury-metallic halide lamps issubstantially as follows: When an initial voltage difference ofsuflicient magnitude is applied to the respective contacts of base 2, ahigh potential exists between starter electrode 10 and arc-electrode 7;as well as between arc-electrodes 6 and 7. The electric field betweenstarter electrode 10 and arc-electrode 7 is suflicient to cause thebreak down of the buffer gas and cause a glow discharge therebetween.Since the lamp is generally in a vertical position and since filler 19is generally in the vicinity of the gap between starter electrode 10 andarc-electrode 7, the initial glow discharge maintained by the buffer gasis sufficient to cause a heating and vaporization of the mercury ofcharge 19. When a sufficient quantity of mercury has been volatilized sothat the conditions of electric field and mercury vapor pressure betweenarc-electrodes 6 and 7 is appropriate, the mercury is dissociated and amercury arc discharge is struck between arc-electrodes 6 and 7. At thispoint, the buffer gas ceases to be of great importance, since thevoltage drop in the arc discharge between arc-electrodes 6 and 7 is muchless than in the glow discharge between starter electrode andarc-electrode 7. The mercury arc between arcelectrode 6 and 7 is ofsufficient temperature to cause the volatilization of the liquid orsolid, but vaporizable, metallic halides within charge 19. These halidesare vaporized and are influenced by the high-temperature mercury arc.The high temperature of the mercury arc, which may be of the order of3000 C., or higher, is sufiicient to cause the dissociation of themetallic halide causing the metallic specie to exist within the arcdischarge. The metallic species is readily raised to an excited state bythe energy within the mercury arc discharge, which causes thecharacteristic radiative transitions of the metallic specie and thecharacteristic line spectra of the metal or metals present as radiatorswithin the arc column.

The line emission by the metallic radiators is most generally theresonance line for each of the materials which is the linecharacteristic of the lowest permitted energy transition from a lowlevel above the ground state to the ground state of the atom.Collision-caused line-broadening between the radiating specie and theatoms of the volatilized mercury within the envelope 3 results in theemission of line-broadened radiation characteristic of the radiatingmetal, which radiation is of high efiiciency and, assuming theappropriate mix of halides has been added, may be essentially whitelight having a chromatically pleasing characteristic.

As is mentioned hereinbefore, lamps operating under the presentlydescribed mechanism are highly effective for emitting high-efficiencychromatically-pleasing light. Unfortunately, however, the metal of thearc-electrodes tends to become sputtered and evaporated from thearcelectrodes and to be deposited upon the electrode walls, greatlydiminishing the light transmissiveness thereof. Additionally, theconstant removal of metal from the arc-electrodes can lead to eventualdestructive dissipation thereof.

It has been found that a vapor transport cycle utilizing the afiinity ofhalogen gases or vapors is useful in reversing such metallic transport.The utilization of such an iodide transport cycle to counteract theeffects of Walldarkening in an incandescent lamp is disclosed andclaimed in the US. Pat. 2,883,571 to Fridrich et al. In accord with thatcycle, the halogen gas added into the incandescent envelope combinedwith metallic deposits upon the envelope wall to form a metal-halogencompound which is dissociated upon contact with the filament, causing areturn of the filament metal thereto with the release of the halogen gaswhich is then free to migrate back to bulb wall to further combine withdeposited metal.

Attempts have been made to utilize the halogen transport cycle toregenerate the arc-electrodes of vapor arc discharge lamps of themercury-metallic iodide type. For some reason, which has not beendetermined, the mere addition of the halogen vapor in the free state tothe charge of envelope 3 has not been effective to cause theregenerative halide cycle to prevent bulb wall blackening and electrodedepletion. One possible cause is that the presence of other metallicspecie, namely the radiating metals, or the presence of the mercuryvapor within the envelope of the lamp may, in some way, cause thehalogen present to combine with other metallic specie rather thandeposited electrode material upon the bulb Wall. Another possibility isthat the deposited metal on the bulb walls is too hot to enter into sucha cycle. Although it is not known precisely why the addition of the freehalide does not function as in the incandescent lamp environment, it isWell established that it does not.

In accord with the present invention, I have discovered that it ispossible to cause the regenerative halide transport cycle to operatewithin a mercury-metallic halide vapor discharge lamp if the halogen isadded to the lamp in the form of the halide of a metal other than thosemetals which so far have been found useful as efficient light radiatorsin this type lamp. Thus, the metallic halide added to cause theoperation of the regenerative cycle may not be an alkali metal halide,an alkaline earth metal halide, a rare earth metal halide, or atransition metal halide. It has been found that when the halides ofmetals of Group I of the Periodic Table such as sodium, potassium, andrubidium are utilized, wall blackening results. Similarly, when metalsof Group II of the Periodic Table such as zinc, cadmium, strontium, andmercury are added in halide form, bulb wall blackening occurs.Similarly, when halides of metals of Group III of the Periodic Tablesuch as scandium, gallium, yttrium, indium, rare earths, and thalliumare added, bulb wall blackening occurs. Likewise, when metallic halidesof metals of Group IVb and Vb of the Periodic Table, such as titanium,zirconium, vanadium, and tantalum are added, bulb wall blackeningoccurs. Similarly, when the halides of transition metals such as iron,nickel, cobalt, and chromium are added, bulb wall blackening occurs.Additionally, when the addition of halide metals of Groups Nb and Vb ofthe Periodic Table are made, as for example the halides of titanium,zirconium, vanadium, and tantalum, these additives react unfavorablywith fused quartz, one envelope material frequently utilized as anenvelope for containing the radiating specie in mercury-metallic halidelamps.

In general, I find that the metals which are suitable for addition inthe halide other than the fluoride to cause the operation of a halogenregenerative cycle, are halides of metals which have a primary valenceof two or greater. These metals will be referred to herein aspoly-valent metals. The use of the word, polyvalent, does not mean toimply all metals which have more than one valence, which are moreproperly referred to as multi-valent metals, but it is meant to implymaterials which have a valence of two, three, or four. The polyvalentmetals utilized in accord with the present invention for addition, ashalides, to the charge of a mercury-metallic halide lamp to cause ahalogen regenerative cycle to occur are polyvalent metals other thanmetals of the alkali metals, alkaline earth metals, the transitionmetals, and the rare earth metals. Preferably, I utilize the halides oftin, lead, antimony, and bismuth, although the halides of germanium andsilicon may also be used to advantage.

In general, the metallic halides added to charge 19 to cause aregenerative halogen cycle to occur within a mercury-metallic halidelamp, should be added in a quantity suflicient, upon volatilizationthereof at lamp operating temperatures, to result in a partial pressureof the halide within the envelope, of approximately 0.1 to torr.

In the operation of lamps in accord with the present invention, thepolyvalent metal halide is volatilized along with the other halides.Although the polyvalent metal of the halide which is added to cause theregenerative halogen cycle to exist, may be observed to contribute somespectroscopic lines to the emission of the lamp, it is not generally ahighly efficient radiator; and it need not enter into the completedissociation and radiative transition which is participated in by thelight emitters. Rather, the polyvalent metal halide must have adissociation characteristic which permits at least partial dissociationthereof at the envelope Wall temperature, to cause the creation of aless halogen-rich polyvalent metallic compound, or to cause the completefreedom of halogen specie at the bulb wall.

Although the chemical reaction which occurs at the bulb wall is notfully understood, it is believed that the reaction is most likely adissociation of the polyvalent metal halide into a very unstable,halogen-rich compound which reacts with the arc-electrode material uponthe interior of the bulb wall to cause the creation of a complexmetallic halogen compound which is dissociated when contacted by thearc-electrode to cause the deposition of arc-electrode materialthereupon and the release of further halogen-rich metallic compoundwhich may migrate to the inner bulb wall surface to further combine withdeposits upon the bulb wall.

Although this mode operation is set forth as one pos sible explanationof the phenomenon in accord with the present invention, if a furtherdescription thereof is later found to be more accurate, it is to beunderstood that the invention is not predicated upon this explanation.It is, however, essential that the polyvalent metallic halide added tocause the halogen regenerative cycle to occur, must undergo at least apartial dissociation at the temperature at the inner portion of the bulbwall in order that the halogen regenerative cycle occur.

An added advantage found in the utilization of the polyvalent metallichalides utilized in accord with the present invention to cause aregenerative cycle within mercury- -metallic halide vapor lamps is that,these lamps, in which sodium is a nearly essential element for obtaininghigh efficiency and good chromatic results, tend to be deleteriouslyaffected by the corrosive action of hot sodium vapor. Thus, for example,if the lamp envelope is of fused quartz, sodium in its elemental form,at high temperature in contact with the quartz, tends to diffuse intothe quartz and attack it chemically. Irrespective of the material fromwhich the lamp is made, metallic sodium at high temperatures tends to beexceedingly destructive to the metal-to-glass or metal-to-ceramic sealswhich surround the electrodes at the point of entry into the envelope.Thus, any contribution which reduces the contact betweendissociation-freed elemental sodium is greatly beneficial in lamps ofthis type. The utilization of the polyvalent halides in accord with thepresent invention, causes the creation, by virtue of the at leastpartial dissociation of the polyvalent metallic halide at the bulb innerwall surface, a nonreducing, oxidizing atmosphere to exist in thevicinity of the bulb wall inner surface, including the portions at whichthe seals are made. This oxidizing atmosphere tends to favor any sodiumwhich may be present thereat existing in a relatively stable compoundform rather than in the highly-reactive elemental form.

Accordingly, the utilization of the polyvalent metallic halides, whichat least partially dissociate at the temperature of the bulb walls underoperating conditions and which create thereat an oxidizing atmosphere,greatly enhances the lamp life in preventing attack of the bulb wallsand bulb seals by highly reactive heated elemental sodium, which is anessential element for high-efficiency, good chromatic characteristicmercury-metallic halide vapor discharge lamps.

The polyvalent metallic halides utilized in accord with the presentinvention must be inorganic halides, since it is found that organichalides are not chemically compatible with the existing system withinthe mercurymetallic halide vapor arc discharge lamp.

In the operation of mercury-metallic halide vapor arc lamps prior to thepresent invention, even in the presence of free-halogen vapor, as forexample, bromine, chlorine, or iodine, in an attempt to make use of thehalogen regenerative cycle, it has been observed that the free halogenacts deleteriously in that it tends to combine with the cooler, lessactive arc-electrode material along the shank of the arc-electrode inthe vicinity of its entry into the envelope, in preference to theelectrode metal on the bulb walls, and to deposit this arc-electrodemate rial at the hotter, more reactive tip of the electrode, rather thanremoving the deposited arc-electrode material from the bulb walls. Thisharmful, free-iodine regenerative cycle does not occur in accord withthe present invention since the polyvalent halides in accord with thepresent invention which results in the useful halide cycle are active tocombine with electrdoe material at the wall, preferably since they aredissociated, at least partially, at the bulb wall by the temperaturethereof.

One lamp constructed in accord with the Present invention operated at a400 watt rating and was substantially as illustrated in the drawing. Theinner envelope 3 had a volume of 18 cc. and contained a charge of 60milligrams of sodium bromide, 50 milligrams of stannous, iodide,milligrams of mercury, and a partial pressure of 18 torr of argon. Thesodium charge resulted in a partial pressure thereof of approximatelyone torr of sodium bromide, the remainder being in excess to maintaincorrect partial pressure in case of sodium depletion. The 50 milligramsof stannous iodide resulted in a partial pressure of approximately 0.5atmosphere of of stannous iodide and contained all of the stannousiodide, with none remaining in excess. The 80 milligrams of mercury wascompletely volatilized in operation and resulted in pressure ofapproximately four atmospheres of mercury. The lamp, as described above,emitted a radiation that had a golden light due to radiation ofcollision-broadened sodium lines and the blue radiation of mercury. Thislamp operated for 1000 hours with no darkening of the bulb walls and,upon cessation of the test, examination revealed substantially no changein the configuration of the arc-electrodes.

In another lamp constructed in accord with the present invention, a 400watt rated lamp having the configuration FIG. 1 and a volume of 18 cc.,contained a charge of 60 milligrams of sodium bromide, 50 milligrams ofstannous iodide, 80 milligrams of mercury, 2 milligrams of thallousiodide, l milligram of indium iodide, and 18 torr of argon. This lampoperated to provide a pleasing white light with no darkening of the bulbwalls or noticeable deterioration of the electrodes.

Another embodiment of the present invention constructed for a 400 wattrating of operation utilized an 18 cc. bulb 3 and contained a charge of60 milligrams of sodium iodide, 5 milligrams of stannous bromide, 80milligrams of mercury, 18 torr of argon, 2 milligrams of thallousiodide, and l milligram of indium iodide. This bulb operated to producea pleasing white light radiation with no darkening of the bulb walls inthe vicinity of the electrodes, or elsewhere, nor any noticeabledeterioration of the arc-electrodes.

Another lamp constructed in accord with the present invention utilized60 milligrams of sodium chloride, 5 milligrams of lead iodide, 18milligrams of mercury, 2 milligrams of thallous iodide, and l milligramof indium iodide in an 18 cc. bulb, rated for 400 watt operation. Thislamp operated to produce a pleasing white emission and no darkening ofthe bulb walls or deterioration of the arc-electrodes.

Another lamp in accord with the present invention utilized an 18 cc.bulb rated for 400 watt operation, as illustrated in the drawing and hada charge of 60 milligrams of sodium iodide, 5 milligrams of antimonyiodide, 80 milligrams of mercury, 2 milligrams of thallous iodide, and 1milligram of indium iodide. The lamp operated to produce a pleasingwhite light with no noticeable blackening of the bulb walls ordeterioration of the arc-electrodes.

Another lamp constructed in accord with the present invention utilizedan 18 cc. bulb and was rated for 400 watt operation. Construction wasessentially that as illustrated in the drawing. The charge 19 within theenvelope contained 60 milligrams of sodium bromide, 10 milligrams ofbismuth trichloride, 80 milligrams of mercury, 2 milligrams of thallousiodide, 1 milligram of indium iodide, and 18 torr of argon. This lampoperated to produce a pleasing white light with no noticeable darkeningof the bulb wall or deterioration of the arc-electrodes.

From the foregoing, it is apparent that I have discovered a new anduseful concept of making improved mercury-metallic halide vapor-arcdischarge lamps wherein inorganic, polyvalent metallic halides of metalshaving a valence of two or greater and excluding metals from the alkalimetal group, the alkaline earth metal group,

the metals of Group III of the Periodic Table including the rare earthmetals, the metals of Group II of the Periodic Table, Group IV!) of thePeriodic Table such as titanium and zirconium, and the metals of GroupVb of the Periodic Table including vanadium and tantalum, and having acharacteristic of at least partial dissociation at the operatingtemperature of the bulb walls of lamps in accord with the invention,namely, a temperature of in excess of 600 C. and no higher than 1200 C.,operate to cause a regenerative halogen transport cycle within the lampsufiicient to prevent the darkening of the bulb walls or the destructionor deterioration of the arc-electrodes by sputtering or evaporationtherefrom.

While the invention has been set forth herein with respect to certainspecific embodiments and examples thereof, many additional modificationsand changes will readily occur to those skilled in the art. Accordingly,by the appended claims, I intend to cover all such modifications andchanges as fall within the true spirit and scope of the presentinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A gaseous arc discharge lamp comprising:

(a) an hermetically sealed, light-transmissive envelope;

(b) a pair of non-liquid arc-electrodes extending Within said envelope;

(c) a quantity of mercury Within said envelope sufficient upon completevaporization thereof to produce within said envelope a mercury pressureof 110 atmospheres;

(d) a vaporizable light producing charge within said envelope,

(d said charge including a halide other than the fluoride of a metalselected from the group consisting of lithium, sodium, cesium, calcium,cadmium, barium, gallium, indium, thallium, mercury, zinc, thorium,vanadium and scandium sufiicient upon partial vaporization thereof atthe equilibrium operating temperature of the lamp to provide a partialpressure of each vaporized metallic halide of approximately 0.1 to 200torr; and

(e) a quantity within said envelope of an inorganic halide, other thanthe fluoride, of a polyvalent metal selected from the group consistingof the metals of Groups IVa and Va of the Periodic Table of theelements,

(e said inorganic halide being at least partly dissociable at theequilibrium operating temperature of the inner surface of said envelopeWall, and being effective to support a halogen transport cycle to keepthe inner surface of said envelope free of sputtered electrode metal andto keep said arc-electrodes from destruction by loss of metal bysputtering and evaporation;

(f) the walls of said envelope being spaced in relation to saidarc-electrodes so that during the operation of the interior of saidenvelope is maintained at a temperature of in excess of 600 C. and nohigher than 1.200 C.

2. The device of claim 1 wherein the polyvalent metal is selected fromthe group consisting of tin, lead, antimony and bismuth.

3. The device of claim 1 wherein the polyvalent metal is tin.

4. The device of claim 3 wherein the inorganic halide which is effectiveto support a regenerative halide cycle is stannous bromide.

5. The device of claim 3 wherein the inorganic halide which is effectiveto support a regenerative halide cycle is stannous iodide.

6. The device of claim 3 wherein the inorganic halide which is effectiveto support a regenerative halide cycle is stannous chloride.

References Cited UNITED STATES PATENTS 3,331,982 7/ 1967 Waymouth313-227 X 3,384,774 5/1968 English 313227 X 3,398,312 8/1968 Edris313227 X FOREIGN PATENTS 900,200 7/ 1962 Great Britain. 274,989 10/ 1964Australia. 1,110,018 4/1968 Great Britain.

JAMES W. LAWRENCE, Primary Examiner D. OREILLY, Assistant Examiner US.Cl. X.R. 313--223. 229

